Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18
Your body is creating and killing about 2.4 million red blood cells per second.
17
The average sperm cell swims at 8 inches per hour.
76
If you are cold you are more likely to be hungry because you use energy to keep warm.
143
The human body contains over a billion miles of DNA.
147
Your thumb is about the same size as your nose.
124